Former Anglo boss David Drumm has agreed to give evidence in a case where widespread "fraud" and "overcharging" by the former toxic bank is alleged, an Irish developer has said in a sworn statement.

An affidavit by John Flynn, the developer that built large parts of Dublin's Smithfield and other major projects, details recent discussions with Mr Drumm.

"In our August 15, 2013, meeting, I told Mr Drumm that we would be subpoenaing him to give evidence in our legal action for fraud in the IBRC/Nama litigation.

"Mr Drumm confirmed, in response, that he would give corroborative evidence to substantiate and verify our allegations in court.

"Mr Drumm and I have discussed a number of things about Anglo," he said.

"One such thing that we have discussed in detail is interest-rate loading by Anglo that resulted in overcharging of interest to Anglo's borrowers."

"Mr Drumm has confirmed and explained to me in our conversations that the rates were fraudulently loaded by Anglo."

The affidavit was filed for a case being taken by Chicago Spire developer Garrett Kelleher against the IBRC in Chicago.

Galway tycoon Declan Ganley also filed a startling affidavit as part of the Kelleher case.

Mr Ganley gives a sworn declaration that he met an Anglo Irish Bank executive who had worked for the bank for many years in 2010 at the executive's office in Stephen's Green where they had "a long discussion".

"He said that it wasn't a great secret within Anglo and that it had been standard practice for many years."

Mr Ganley also stated: "I have to say that it was my clear understanding at the time that [the named executive] was motivated by his concern for the direction of the country and the risk to the national interest. He left me with a very positive impression."

When Mr Ganley expressed disbelief that such a practice could have existed without being spotted by a regulator or auditor, he claims the Anglo executive said he had a copy of internal documents from Anglo which appeared to confirm that the practice existed.

The Sunday Independent understands that on Monday of last week Mr Ganley also lodged a formal complaint to the Garda Bureau of Fraud Investigation for "fraudulent overcharging". Mr Ganley declined to comment.

Mr Flynn also states that a forensic accounting firm hired by him to review the interest charged on loans with Anglo showed, "every account reviewed was found to have involved overcharging as a result of increasing or 'loading' interest rates above the rates that the borrowers agreed to pay. The loading ranged from 0.5 per cent to .05 per cent".

"The foregoing results and analysis [by Flynn's forensic accountants] support that the overcharging ... could exceed $1.2bn," he states.

The former Anglo executive who spoke to Mr Ganley did not respond to calls and texts to his mobile number on Thursday and Friday.

Mr Drumm did not respond to emails to either his personal email or his lawyer's email.